Patent GB-380108-A (GB)
Title: Improvements in cranes and like lifting appliances
IPC: B66C23/90
Filed: 1931-06-02
Abstract: 380,108. Jib cranes. WYLIE, H. N., 5, Clement's Inn, London. June 2, 1931. Nos. 16061 and 20392. [Class 78 (iv).] In a safety device for a luffing crane the varying tension in the load rope, or in the jibsupporting rope, due to the maximum safe load at any radius, is caused to exert the same force on a load-sensitive unit. The device may signal the maximum safe load, and other loads related thereto ; it may trip a switch to cut off power, apply a brake, &c. ; and it may be arranged to signal under full load at any radius less than the maximum radius permissible with full load. The arrangement may be such that maximum safe load at any radius corresponds to an overturning moment either constant or decreasing with increase of radius. As shown in Fig. 1, the load rope A passes over a guidesheave C1 mounted on a shaft C on a tension member E pivoted at H, and the tension in the member E is transmitted through a loadsensitive unit U. The shaft C bears against a guide G on the mast or is connected to the mast by radius rods. The guide G or radius rod is arranged so that over the luffing range predetermined safe loads varying with the radius will produce the same tension in the loadsensitive unit U. A graphical construction for determining the position of the guide G is given. A barrel or pulley F is mounted to engage the load rope on luffing in to the maximum radius permissible at full load, so that at any smaller radius the inclination of the rope A passing round the sheave C1 is unaltered and the signal is given at full load. As shown in Fig. 3, the sheave C1 is mounted between radius links 5 pivoted at 6 on the mast M, and pivotally connected at 7 to bolts 1 which are connected bv a cross-bar 8 supported on compression springs 2 bearing on a fixed cross-bar 3. The springs may be initially under stress. The bar 8 actuates a lever 10 and indicating pointer (not shown), and may control an electric circuit to give a sound signal at maximum safe load and other signals at other loads. The pair of links 5 are rigidly connected by a torqueresisting tube 12. As shown in Fig. 5, the sheave C1 is mounted in a rigid frame E and the tension in the frame operates a load-sensitive unit U of the kind described in Specification 377,209. The spindle C bears on guides G when the radius is greater than that permissible with full load on the crane, and on guides G1 at smaller radii when the device U is required to signal at the full load irrespective of the radius. In suitable cases, the guides G, or G and G1, may be omitted. As shown in Fig. 8, the jib-head pulley B1 is mounted on an axis B in levers 5 pivoted at 6 in the jib and supported by the load-sensitive unit U. The device U is arranged so that the resultant of the forces in the two branches A, A1 of the load rope at maximum safe load is balanced by a constant force on the device U and a variable force in the direction B-6. As the jib moves towards the vertical, the vertical run A1 of the load rope bears against a pulley F on the jib so that on further luffing in the angle between A and A1 remains substantially constant and the device U signals under full load. As applied to the jib-supporting rope, the pulley R, Fig. 1, may be supported by a load-sensitive unit ; the force in the rope Q due to maximum safe load is usually nearly constant for radii equal to or greater than the maximum radius permissible under full load, and the pulley F is arranged to bear on the rope Q under these conditions. In a modification, not illustrated, the luffing rope passes round a pulley supported on or from the jib head and this pulley is supported by a load-sensitive unit on the jib as in Fig. 8. The second Provisional Specification describes also the production of two distinct sound signals in succession, as by a bell, and a horn or whistle ; and the production of a sound or light signal as conditions approach the limit of safety, and the closing of a switch to cut off power when the limiting load is exceeded.